Re: [PATCH] drm: Provide a driver hook for drm_dev_release()

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Chris,

Thank you for the patch.

On Thursday 08 Dec 2016 08:18:40 Chris Wilson wrote:
> Some state is coupled into the device lifetime outside of the
> load/unload timeframe and requires teardown during final unreference
> from drm_dev_release(). For example, dmabufs hold both a device and
> module reference and may live longer than expected (i.e. the current
> pattern of the driver tearing down its state and then releasing a
> reference to the drm device) and yet touch driver private state when
> destroyed.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/drm_drv.c | 3 +++
>  include/drm/drm_drv.h     | 8 ++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index f74b7d06ec01..f945bbcc8eb3 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -595,6 +595,9 @@ static void drm_dev_release(struct kref *ref)
>  {
>  	struct drm_device *dev = container_of(ref, struct drm_device, ref);
> 
> +	if (dev->driver->release)
> +		dev->driver->release(dev);
> +
>  	if (drm_core_check_feature(dev, DRIVER_GEM))
>  		drm_gem_destroy(dev);

For drivers embedding the drm_device structure, you should only call 
.release() at the very end of this function, as the callback will free memory, 
including the embedded struct drm_device. Similarly, the kfree() at the end 
should be made conditional. Or, better, you could implement a release function 
that just wraps kfree(), and set it as the release handler in drm_dev_alloc(). 
Drivers using drm_dev_init() would need to provide their own release handler.

> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> index c4fc49583dc0..554104ccb939 100644
> --- a/include/drm/drm_drv.h
> +++ b/include/drm/drm_drv.h
> @@ -71,6 +71,14 @@ struct drm_driver {
>  	void (*postclose) (struct drm_device *, struct drm_file *);
>  	void (*lastclose) (struct drm_device *);
>  	int (*unload) (struct drm_device *);
> +	/**
> +	 * @release:
> +	 *
> +	 * Optional callback for destroying device state after the final
> +	 * reference is released, i.e. the device is being destroyed.
> +	 */
> +	void (*release) (struct drm_device *);
> +
>  	int (*dma_ioctl) (struct drm_device *dev, void *data, struct drm_file
> *file_priv);
> 	int (*dma_quiescent) (struct drm_device *);
>  	int (*context_dtor) (struct drm_device *dev, int context);

-- 
Regards,

Laurent Pinchart

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